Anti-p stopping power in hydrogen below 1 MeV and the anti-p 4He metastable state.

The stopping power of H-2 for psBAR was measured in the pBAR energy interval 1 keV divided-by 120 keV using a low density gas target (rho/rho(o) = 10(-3) divided-by 10(-2), rho(o) being the H2 density at STP) with the OBELIX spectrometer at the LEAR of CERN. Furthermore, the formation of metastable states in the pBAR He-4 interaction at rest, having a mean life of the order of 3 mus, was investigated at six target gas pressures (3 atm and 400, 250, 200, 150, 50 mbar). The influence of contaminants (like H-2, Ne, Ar, N2 and Xe) on the life of such metastable states was examined at the target gas pressure of 3 atm.